Image forming apparatus

Abstract

This reduces power consumption in the fuser unit and ensures that the toner image is reliably fixed to the paper. [Solution] The control unit obtains the total pixel value by summing the pixel values ​​of each of the multiple pixels contained in each of the N × M blocks into which the image data has been divided (S102). The N × M blocks are arranged in the paper transport direction of the transport unit in an N-order direction and in an orthogonal direction perpendicular to the transport direction. The control unit calculates the m-th mean value by averaging the sum of the total pixel values ​​of the N blocks arranged in the transport direction at the m-th block position (where m is an integer from 1 to M-1) in the orthogonal direction with the sum of the total pixel values ​​of the N blocks arranged in the transport direction at the (m+1)-th block position in the orthogonal direction (S103, S104). Based on the m-th mean value, the fixing temperature of the fixing unit is determined (S105~S107).

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, and particularly to a technique for controlling the fixing temperature.

Background Art

[0002] An electrophotographic image forming apparatus includes an image forming unit that forms a toner image on a sheet based on image data, and a fixing unit that heats and pressurizes the sheet on which the toner image is formed. In such an image forming apparatus, it is required to reduce power consumption while maintaining a fixing temperature for reliably fixing the toner image on the sheet. In the adjustment of the fixing temperature according to the toner loading amount, since the toner loading amount has a high correlation with the pixel value of the image data, a technique for calculating the toner loading amount based on the pixel value and determining the fixing temperature is known.

[0003] As a technique for controlling the fixing temperature according to the toner loading amount, there is a technique disclosed in Patent Document 1. In the technique disclosed in Patent Document 1, first, an image is divided into meshes, and for each mesh, count information (the total toner loading amount of a plurality of pixels) of the toner loading amount of a plurality of pixels in the mesh and the position information of the mesh are acquired and stored in a memory. Next, N×M meshes are set as one region, and while shifting the position by one mesh at a time, a location with a large toner loading amount is searched over the entire image, and the fixing temperature is determined using the search result.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the technology disclosed in Patent Document 1 requires additional hardware in addition to a counting unit that counts the amount of toner applied to each of the multiple meshes, as well as a determination unit that determines the position corresponding to each of the multiple meshes. The determination unit is required for the maximum number of mesh positions that can be determined. For this reason, for example, when the page size of the image data is large, such as in banner printing, the number of meshes becomes enormous, and the additional hardware resources required become enormous.

[0006] By the way, even with the same image rendering content, the toner load count value varies greatly depending on the positional relationship between the image rendering area and the mesh on the page. Therefore, it is difficult to determine the fixing temperature of the fuser unit that will suppress power consumption in the fuser unit and reliably fix the toner image to the paper based on the toner load count value.

[0007] This invention has been made in view of the above circumstances, and aims to reduce power consumption in the fixing unit and ensure that the toner image is reliably fixed to the paper, regardless of the positional relationship between the image drawing area on the page and the blocks into which the image data is divided. [Means for solving the problem]

[0008] An image forming apparatus according to one aspect of the present invention comprises: an image forming unit that forms a toner image on paper based on image data; a fixing unit that heats and pressurizes the paper on which the toner image has been formed; a transport unit that transports the paper to the image forming unit and the fixing unit; and a control unit that controls the fixing temperature of the fixing unit, wherein the control unit performs a total pixel value acquisition process to acquire a total pixel value by summing the pixel values ​​of each of the multiple pixels contained in each of the N × M blocks obtained by dividing the image data into predetermined sizes, and the N × M blocks are arranged in the transport direction of the paper of the transport unit and in an orthogonal direction perpendicular to the transport direction, and m in the orthogonal direction (m is 1 or less An average value calculation process is performed to calculate the m-th average value by averaging the sum of the total pixel values ​​of each of the N blocks lined up in the transport direction at the (M-1 or less integer)-th block position and the sum of the total pixel values ​​of each of the N blocks lined up in the transport direction at the (m+1)-th block position in the orthogonal direction. If at least one of the m-th average values ​​exceeds a predetermined threshold, the fixing temperature of the fixing unit is determined to a predetermined first fixing temperature. If none of the m-th average values ​​exceed the predetermined threshold, a fixing temperature determination process is performed to determine the fixing temperature of the fixing unit to a fixing temperature lower than the first fixing temperature, which is predetermined according to the m-th average values.

[0009] An image forming apparatus according to another aspect of the present invention comprises: an image forming unit that forms a toner image on paper using a plurality of colors based on image data; a fixing unit that heats and pressurizes the paper on which the toner image has been formed; a transport unit that transports the paper to the image forming unit and the fixing unit; and a control unit that controls the fixing temperature of the fixing unit, wherein the control unit performs a total pixel value acquisition process to acquire a total pixel value for each of the plurality of pixels of a given color in each of the N × M blocks obtained by dividing the image data into predetermined sizes, and the N × M blocks are arranged in the transport direction of the paper of the transport unit and in an orthogonal direction perpendicular to the transport direction, and m (where m is 1 or more and M) in the orthogonal direction. An average value calculation process is performed to calculate the m-average value by averaging the sum of the total pixel values ​​of each of the multiple colors in each of the N blocks arranged in the transport direction at the (-1 or less integer)th block position and the sum of the total pixel values ​​of each of the multiple colors in each of the N blocks arranged in the transport direction at the (m+1)th block position in the orthogonal direction. If at least one of the m-average values ​​exceeds a predetermined threshold, the fixing temperature of the fixing unit is determined to a predetermined first fixing temperature. If none of the m-average values ​​exceed the predetermined threshold, a fixing temperature determination process is performed to determine the fixing temperature of the fixing unit to a fixing temperature lower than the first fixing temperature, which is predetermined according to the m-average values. [Effects of the Invention]

[0010] According to the present invention, the fixing temperature of the fixing unit is determined using the m-th mean value, which is the average of the sum of the pixel values ​​obtained by summing the pixel values ​​of each of the multiple pixels contained in each of the N blocks arranged in the transport direction at the m-th block position in the orthogonal direction (where m is an integer from 1 to M-1) or the sum of the pixel values ​​obtained by summing the pixel values ​​of each of the multiple pixels contained in each of the N blocks arranged in the transport direction at the (m+1)-th block position in the orthogonal direction or the sum of the pixel values ​​obtained by summing the pixel values ​​of each of the multiple pixels contained in each of the N blocks arranged in the transport direction at the m-th block position in the orthogonal direction. The maximum variation in the m-th mean value is suppressed regardless of the positional relationship between the image drawing area on the page and the blocks into which the image data is divided. Therefore, by controlling the fixing temperature of the fixing unit, power consumption in the fixing unit can be reduced and the toner image can be reliably fixed to the paper. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic front cross-sectional view showing an image forming apparatus according to one embodiment of the present invention. [Figure 2] Figure 1 is a block diagram showing the internal configuration of the image forming apparatus. [Figure 3] Figure 2 is a block diagram showing the functional configuration of the system controller and engine controller. [Figure 4] This figure illustrates the control of the fixing temperature in the fixing section of Figure 2. [Figure 5] This figure illustrates the control of the fixing temperature in the fixing section of Figure 2. [Figure 6] This figure illustrates the control of the fixing temperature in the fixing section of Figure 2. [Figure 7] Figure 3 is a flowchart showing the processing procedure for determining the fixing temperature of the fixing unit by the fixing control unit. [Figure 8] Figure 3 is a flowchart showing the processing procedure for determining the fixing temperature of the fixing unit by the fixing control unit. [Figure 9]It is a diagram showing the image formation flow of the image forming apparatus of FIG. 1.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[0013] [Configuration of Image Forming Apparatus 1] FIG. 1 is a front sectional view showing an outline of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram showing an internal configuration of the image forming apparatus 1 of FIG. 1. The image forming apparatus 1 is a multifunction device having a plurality of functions such as a copying function, a transmission function, a printer function, and a facsimile function.

[0014] As shown in FIG. 1, the image forming apparatus 1 includes a document conveyance unit 6, an image reading unit 11, an image forming unit 12, a fixing unit 13, a paper feeding unit 14, a display unit 15, an operation unit 16, and a conveyance unit 17.

[0015] The document conveyance unit 6 conveys the documents placed on the document table one by one to the reading position of the image reading unit 11. The document conveyance unit 6 is configured to be able to open and close the platen glass 7 by rotating in the vertical direction around the support shaft on the back side of the paper surface in FIG. 1. The document conveyance unit 6 also functions as a cover that presses the document on the platen glass 7 from above.

[0016] The image reading unit 11 is a scanner that optically reads a document and generates image data indicating the document image. The image reading unit 11 reads the document conveyed by the document conveyance unit 6 or the document placed on the platen glass 7.

[0017] The image forming unit 12 includes a photoreceptor drum, a charging device, an exposure device, a developing device, and a transfer device. The exposure device includes an LSU (Laser Scanning Unit) 12A (see FIG. 3). The image forming unit 12 forms a toner image on the paper P conveyed along the conveyance path T by the conveyance unit 17 based on the image data. For example, in the case of color printing, the image forming unit 12 forms a color toner image on the paper P using four colors (cyan, magenta, yellow, and black) based on the image data, and in the case of monochrome printing, forms a monochrome toner image on the paper P using one color (black) based on the image data.

[0018] The fixing unit 13 heats and presses the paper P on which the toner image is formed to fix the toner image on the paper P. The paper P on which the toner image is fixed is discharged to the discharge tray 8.

[0019] The paper feeding unit 14 includes a manual feed tray and a plurality of paper feed cassettes. The paper feeding unit 14 pulls out the paper P stored in any of the plurality of paper feed cassettes or the paper placed on the manual feed tray one by one by a pickup roller and feeds it to the conveyance path T. Note that the paper P is not limited to a paper medium and may be, for example, an OHP (Overhead Projector) sheet.

[0020] The display unit 15 includes a liquid crystal display or an organic EL (Organic Light-Emitting Diode) display. The display unit 15 displays various screens.

[0021] As shown in FIG. 2, the operation unit 16 includes a plurality of hard keys such as a start key 16A for inputting an execution start instruction for copy processing, scan processing, etc., and a touch panel 16B disposed over the display unit 15. Instructions from the user are input to the operation unit 16.

[0022] The transport unit 17 includes a transport roller pair 17A, an ejection roller pair 17B, a registration roller 17C, etc., and a transport motor. When the transport roller pair 17A, the ejection roller pair 17B, and the registration roller 17C, etc. are rotated by the drive of the transport motor, the paper P fed by the paper feeding unit 14 is transported along the transport path T to the image forming unit 12 and the fixing unit 13, etc.

[0023] As shown in Figure 2, the image forming apparatus 1 further includes a control unit 100, a storage unit 18, an image processing unit 19, an image memory 20, a facsimile communication unit 21, and a communication unit 22.

[0024] The control unit 100 is electrically connected to the document transport unit 6, image reading unit 11, image forming unit 12, fixing unit 13, paper feeding unit 14, display unit 15, operation unit 16, transport unit 17, storage unit 18, image processing unit 19, image memory 20, facsimile communication unit 21, and communication unit 22.

[0025] The control unit 100 controls the operation of each part of the image forming apparatus 1. The control unit 100 includes a print controller 110 and an engine controller 120. The print controller 110 and the engine controller 120 can communicate with each other via a bus through a communication interface.

[0026] The storage unit 18 is a large-capacity storage device for storing various types of data, such as an HDD (Hard Disk Drive) or SSD (Solid State Drive), and stores various computer programs, such as various control programs, for realizing the operation of the image forming apparatus 1. One of the control programs installed in the storage unit 18 is a fixing temperature control program for controlling the fixing temperature of the fixing unit 13.

[0027] The image processing unit 19 is a circuit that performs image processing on image data. The image processing unit 19 includes a system controller 190. The image memory 20 temporarily stores the image data. The facsimile communication unit 21 transmits and receives image data via a public telephone line.

[0028] The communication unit 22 includes a communication module such as a LAN (Local Area Network) board. The control unit 100 communicates data with external devices such as a host PC (Personal Computer) 23 connected to the network via the communication unit 22.

[0029] Each part of the image forming apparatus 1 is connected to a power supply. When the user turns on the power, power is supplied from the power supply to each part of the image forming apparatus 1.

[0030] [Control of fixing temperature] In this embodiment, the image data is divided into N × M blocks of a predetermined size, and N blocks are arranged in a predetermined first direction, while M blocks are arranged in a second direction perpendicular to the first direction. In the case of normal printing, the first and second directions are the paper transport direction of the transport unit 17 and the direction perpendicular to the transport direction, and hereafter, the paper transport direction of the transport unit 17 and the direction perpendicular to the transport direction will be referred to as the "sub-scanning direction" and the "main scanning direction" as appropriate.

[0031] The amount of heat removed from the heating element of the fuser unit 13 is determined by the amount of toner applied to the entire page in the sub-scanning direction at the position in the main scanning direction. Conventionally, heating is performed to a temperature where fixing failure does not occur even with the maximum amount of toner applied. However, if the amount of toner applied to the entire page in the sub-scanning direction at the position in the main scanning direction can be known before the paper P reaches the heating element of the fuser unit 13, the fixing temperature can be controlled according to the amount of toner applied to the entire page in the sub-scanning direction at the position in the main scanning direction. In the case of continuous printing, the heating element is reheated between sheets of paper P to prepare for the next print.

[0032] For example, when solid CMYK colored areas are printed as shown in Figure 4(A), the amount of toner applied to the entire page in the sub-scanning direction at the main scanning direction is large, requiring a large amount of heat for fixing, thus necessitating a higher fixing temperature for the fuser unit 13. In the case of a black text document as shown in Figure 4(B), the amount of toner applied to the entire page in the sub-scanning direction at the main scanning direction is small, requiring less heat for fixing, and thus allowing for a lower fixing temperature for the fuser unit 13.

[0033] Furthermore, for example, if the block size is 5.4 mm x 5.4 mm, and the image data contains solid patches with a width of two or more blocks in the main scanning direction, the maximum print rate among the sub-scanning directions for the entire page at multiple main scanning positions will not change, regardless of the positional relationship between the solid patch and the blocks in the main scanning direction. On the other hand, if the image data contains solid patches with a width of less than one block in the main scanning direction, the maximum print rate among the sub-scanning directions for the entire page at multiple main scanning positions may fluctuate by up to twice (up to 50%) depending on the positional relationship between the solid patch and the blocks in the main scanning direction. Also, if the image data contains solid patches with a width of one or more blocks but less than two blocks in the main scanning direction, the maximum print rate among the sub-scanning directions for the entire page at multiple main scanning positions may fluctuate by up to 100 - (number of blocks in the main scanning direction of the solid patch) / 2 × 100 (%) depending on the positional relationship between the solid patch and the blocks in the main scanning direction. For example, if the width of a solid patch in the main scanning direction is 1.5 blocks, then if the block boundary is in the middle of the solid patch, it will be divided into two 0.75 blocks and one 0.75 block. If the block boundary is at the 2 / 3 position, it will be divided into one block and one 0.5 blocks. As a result, the maximum print density differs by 25% between the two cases. Therefore, it is difficult to use this as a control parameter for the fixing temperature of the fixing unit 13.

[0034] For example, suppose the image data is divided into N=10 sections in the main scanning direction and M=10 sections in the sub-scanning direction. In this case, for example, if the width of the main scanning direction is 27mm x 27mm, which is four times the block size, the maximum print rate among the print rates of the entire page in the sub-scanning direction at multiple main scanning positions remains constant at 40%, as shown in Figures 5(A-1) and (A-2). On the other hand, if the width of the main scanning direction is 5.4mm x 27mm, which is one time the block size, the maximum print rate when the solid patch does not cross a block boundary in the main scanning direction, as shown in Figure 5(B-1), is 40%, and the maximum print rate when the solid patch crosses a block boundary in its center in the main scanning direction, as shown in Figure 5(B-2), is 20%. Note that in Figure 5, the smallest square corresponds to a block.

[0035] For example, in the case of a solid patch of 27 mm × 27 mm, where the width in the main scanning direction is greater than or equal to two block sizes, the maximum average print rate among the average print rates obtained by averaging the print rates at two consecutive positions in the main scanning direction is 40 (%), as shown in Figures 5(A-1) and (A-2). Furthermore, in the case of a solid patch of 5.4 mm × 27 mm, where the width in the main scanning direction is less than two block sizes, the maximum average print rate among the average print rates obtained by averaging the print rates at two consecutive positions in the main scanning direction is 20 (%), as shown in Figures 5(B-1) and (B-2). Thus, regardless of the positional relationship between the solid patch and the blocks in the main scanning direction, the maximum average print rate among the average print rates obtained by averaging the print rates at two consecutive positions in the main scanning direction does not fluctuate. Therefore, it is suitable for use as a control parameter for the fixing temperature of the fixing unit 13.

[0036] In color printing, for example, when the solid patches of each CMK color shown in Figure 6(A) are arranged in different sub-scanning directions at the same main scanning direction, and when the solid patches of each CMK color shown in Figure 6(B) are located in the same sub-scanning direction at the same main scanning direction, the maximum print coverage in the sub-scanning direction for the entire page at the main scanning direction is the same at 50%, but the maximum print coverage for blocks is different, at 100% in the former case and 300% in the latter case. Therefore, the amount of heat required for fixing is different.

[0037] Based on the above, the fixing temperature determination process for the fixing unit 13 is performed as shown in the flowcharts in Figures 7 and 8.

[0038] [Configuration of System Controller 190] The system controller 190 includes a processor, RAM (Random Access Memory), and ROM (Read Only Memory). The processor is, for example, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), or an ASIC (Application Specific Integrated Circuit).

[0039] The system controller 190 functions as an image generation unit 191, a color conversion unit 192, a pixel value count unit 193, a count value transfer unit 194, a rotation / aggregation unit 195, a correction processing unit 196, and a screen processing unit 197, as shown in Figure 3, when the control program stored in the ROM or storage unit 18 is executed by the processor.

[0040] The system controller 190 may be configured using logic circuits rather than relying on operation based on a control program.

[0041] When the image generation unit 191 receives a print command written in PDL (Page Description Language) from, for example, the host PC 23 via the communication unit 22, it executes RIP (Raster Image Processor) processing to generate color-represented raster data based on the print command. The image generation unit 191 divides the generated raster data into N × M blocks of a predetermined size, which serve as image processing units, and stores them in the page memory area of ​​the image memory 20. The color conversion unit 192, pixel value count unit 193, count value transfer unit 195, rotation / aggregation unit 195, correction processing unit 196, and screen processing unit 197, which are located after the image generation unit 191, process the data in block units. The size of the blocks is not particularly limited. For example, if the size of each block is 128 × 128 pixels and the print resolution is 600 dpi (dots per inch), the size of the image corresponding to each block in the printed material will be 5.4 × 5.4 mm.

[0042] In the case of color printing, the color conversion unit 192 generates image data for four planes corresponding to each of the CMYK (cyan, magenta, yellow, and black) colors based on the raster data stored in the page memory area of ​​the image memory 20, and outputs it to the pixel value count unit 193. In the case of monochrome printing, the color conversion unit 192 generates image data for one plane corresponding to the K color based on the raster data, and outputs it to the pixel value count unit 193.

[0043] The pixel value counting unit 193 performs the following processing in the case of color printing.

[0044] The pixel value counting unit 193, based on the CMYK image data input from the color conversion unit 192, counts the pixel values ​​of each of the multiple pixels included in each of the N×M blocks for each CMYK color. In other words, the pixel value counting unit 193 obtains the total pixel value of each color by summing the pixel values ​​of each of the multiple pixels included in each of the N×M blocks for each CMYK color. For example, if the pixel values ​​of each CMYK color in pixel 1 are C1, M1, Y1, K1, the pixel values ​​of each CMYK color in pixel 2 are C2, M2, Y2, K2, the pixel values ​​of each CMYK color in pixel 3 are C3, M3, Y3, K3, ..., the pixel value counting unit 193 counts C1, C2, C3, ... in order for the C color (and obtains the total pixel value of the C color C1 + C2 + C3 + ...). (obtained), count M1, M2, M3, ... in order for the M color (obtain the total pixel value of the M color M1+M2+M3+...), count Y1, Y2, Y3, ... in order for the Y color (obtain the total pixel value of the Y color Y1+Y2+Y3+...), and count K1, K2, K3, ... in order for the K color (obtain the total pixel value of the K color K1+K2+K3+...).

[0045] Furthermore, the pixel value counting unit 193 counts the CMYK pixel values ​​of each of the multiple pixels contained in each of the N×M blocks, based on the CMYK image data input from the color conversion unit 192. In other words, the pixel value counting unit 193 obtains the total pixel value for all colors (total pixel value for all colors) by summing the CMYK pixel values ​​of each of the multiple pixels contained in each of the N×M blocks. For example, if the pixel values ​​for each CMYK color of pixel 1 in a block are C1, M1, Y1, K1, the pixel values ​​for each CMYK color of pixel 2 are C2, M2, Y2, K2, and the pixel values ​​for each CMYK color of pixel 3 are C3, M3, Y3, K3, ..., the pixel value counting unit 193 counts C1, M1, Y1, K1, C2, M2, Y2, K2, C3, M3, Y3, K3, ... in order (to obtain the total pixel value for all colors C1+M1+Y1+K1+C2+M2+Y2+K2+C3+M3+Y3+K3+...).

[0046] The pixel value counting unit 193 then outputs each count value (total pixel value of C color, total pixel value of M color, total pixel value of Y color, total pixel value of K color, total pixel value of all colors) for each of the N × M blocks to the count value transfer unit 194 in a predetermined order (for example, C color, M color, Y color, K color, and all colors).

[0047] Furthermore, the pixel value counting unit 193 stores the image data for each CMYK plane input from the color conversion unit 192 in the page memory area of ​​the image memory 20.

[0048] The above describes the processing of the pixel value counting unit 193 in the case of color printing.

[0049] The pixel value counting unit 193 performs the following processing in the case of monochrome printing.

[0050] The pixel value counting unit 193 counts the K-color pixel values ​​of each of the multiple pixels contained in each of the N × M blocks, based on the K-plane image data input from the color conversion unit 192. In other words, the pixel value counting unit 193 obtains the total K-color pixel value by summing the K-color pixel values ​​of each of the multiple pixels contained in each of the N × M blocks. For example, if the K-color pixel value of pixel 1 in a block is K1, the K-color pixel value of pixel 2 is K2, the K-color pixel value of pixel 3 is K3, ..., the pixel value counting unit 193 counts K1, K2, K3, ... in order for each K-color (obtaining the total K-color pixel value K1 + K2 + K3 + ...).

[0051] The pixel value counting unit 193 then outputs the count values ​​(total pixel values ​​of the K color) for N × M blocks to the count value transfer unit 194 in a predetermined order.

[0052] Furthermore, the pixel value counting unit 193 stores the K-plane image data input from the color conversion unit 192 in the page memory area of ​​the image memory 20.

[0053] The above describes the processing of the pixel value counting unit 193 in the case of monochrome printing.

[0054] The pixel value counting unit 193 may include a counter circuit for acquiring the total pixel value of C color, a counter circuit for acquiring the total pixel value of M color, a counter circuit for acquiring the total pixel value of Y color, and a counter circuit for acquiring the total pixel value of K color, as well as a counter circuit for acquiring the total pixel value of all colors. The number of bits in each counter circuit can be determined based on the gradation of the pixels and the number of pixels included in the block.

[0055] In the case of color printing, the count value transfer unit 194 receives the count values ​​of N × M blocks (total pixel values ​​for C color, total pixel values ​​for M color, total pixel values ​​for Y color, total pixel values ​​for K color, and total pixel value for all colors) from the pixel value count unit 193 in a predetermined order. The count value transfer unit 194 stores the count values ​​of each block, which are input from the pixel value count unit 193 in a predetermined order, into the SRAM (Static Random Access Memory) of the system controller 190 in the order they were input. The count value transfer unit 194 then outputs an interrupt signal to the print controller 110 when it has stored the count values ​​of a predetermined number of blocks in the SRAM. When the interrupt signal is received, the print controller 110 reads the count values ​​of a predetermined number of blocks stored in the SRAM all at once and stores the read count values ​​of a predetermined number of blocks in a consecutive address in the image memory 20 in the order they were stored in the SRAM.

[0056] In the case of monochrome printing, the count value transfer unit 194 receives the count values ​​(total pixel values ​​of K color) of N x M blocks from the pixel value count unit 193 in a predetermined order. The count value transfer unit 194 stores the count values ​​of each block, which are input from the pixel value count unit 193 in a predetermined order, into the SRAM of the system controller 190 in the order they were input. The count value transfer unit 194 then outputs an interrupt signal to the print controller 110 when it has stored the count values ​​of a predetermined number of blocks in the SRAM. When the interrupt signal is received, the print controller 110 reads the count values ​​of a predetermined number of blocks stored in the SRAM all at once and stores the read count values ​​of the predetermined number of blocks in a predetermined order in the order they were stored in the SRAM at consecutive addresses in the image memory 20.

[0057] This reduces the number of read operations compared to when the print controller 110 reads the count value for each block. It also prevents an increase in hardware resources compared to when a buffer large enough to store the count values ​​of all blocks (i.e., a number that can accommodate the maximum size of image data) is prepared in advance. Furthermore, since the count values ​​are stored in consecutive addresses of the image memory 20 according to a predetermined order, the fixing control unit 123, described later, can sum the total pixel values ​​of each of the N blocks arranged in the sub-scan direction at the position in the main operation direction without requiring any special hardware resources to determine the position of the blocks.

[0058] The rotation and aggregation unit 195, in the case of color printing, refers to the image data of each CMYK plane stored in the page memory area of ​​the image memory 20, and in the case of monochrome printing, refers to the image data of the K plane stored in the page memory area of ​​the image memory 20, reads block-unit image data from the image memory 20 while controlling the reading order, and performs at least one of rotation processing and aggregation processing by rearranging the read block-unit image data according to the settings received via the operation unit 16.

[0059] The correction processing unit 196 performs correction processing, such as edge processing and gamma correction, on the block-level image data in the order in which the processing by the rotation and aggregation unit 195 is completed.

[0060] The screen processing unit 197 performs screen processing on block-level image data in the order that processing by the correction processing unit 196 is completed. The screen processing unit 197 converts the block-level image data for one page that has been screen processed into final drawing data and stores it in the image memory 20, which functions as a buffer.

[0061] [Configuration of Print Controller 110] The print controller 110 includes a processor, RAM, and ROM. The print controller 110 controls the operation of the engine controller 120, etc., by executing a control program stored in the ROM or HDD 18 through the processor.

[0062] For example, the print controller 110 outputs various command signals to the engine controller 120 to perform image forming operations. The print controller 110 may also be configured using logic circuits, rather than relying on a control program.

[0063] [Engine Controller 120 Configuration] The engine controller 120 controls the image forming operation of the image forming apparatus 1. The engine controller 120 includes a processor, RAM, and ROM.

[0064] The engine controller 120 functions as a print position adjustment unit 121, a light emission control unit 122, a fixing control unit 123, a transport control unit 124, and an image formation control unit 125, as shown in Figure 3, when the control program stored in the ROM or HDD 18 is executed by the processor.

[0065] The engine controller 120 may be configured using logic circuits rather than relying on operation based on a control program.

[0066] The print position adjustment unit 121 reads drawing data from the image memory 20 and, according to the settings received via the operation unit 16, performs at least one of the following on the read drawing data: image position adjustment processing and margin addition processing.

[0067] The light emission control unit 122 controls the light emission of the LSU 12A by switching the on / off status of the lighting signal based on drawing data from which at least one of the image position adjustment process and margin addition process has been performed.

[0068] The fuser control unit 123 executes a fuser temperature control program stored in the memory unit 18 for controlling the fuser temperature of the fuser unit 13. The N × M blocks are arranged in a sequence of N in the transport direction (sub-scanning direction) of the paper P of the transport unit 17, and in a sequence of M in the orthogonal direction (main scanning direction) perpendicular to the transport direction. In the case of color printing, the total pixel values ​​of each block (total pixel values ​​for C color, M color, Y color, K color, and total pixel values ​​for all colors) are stored in consecutive addresses of the image memory 20 according to a predetermined order, so the fuser control unit 123 can read the total pixel values ​​of each block from the image memory 20 based on the predetermined order. In the case of monochrome printing, the total pixel values ​​for the K color of each block are stored in consecutive addresses of the image memory 20 according to a predetermined order, so the fuser control unit 123 can read the total pixel values ​​for the K color of each block from the image memory 20 based on the predetermined order.

[0069] The fixing control unit 123 performs the following processing in the case of color printing.

[0070] The fixing control unit 123 obtains the total pixel value for each CMYK color stored in the image memory 20, as well as the total pixel value for all colors, for each of the N × M blocks from the image memory 20.

[0071] If at least one of the total pixel values ​​of all colors in the N×M blocks exceeds a predetermined threshold (hereinafter referred to as the "first threshold"), the fixing control unit 123 determines the fixing temperature of the fixing unit 13 based on the total pixel values ​​of all colors in the N×M blocks. In this embodiment, the fixing control unit 123 determines the fixing temperature to a predetermined fixing temperature (hereinafter referred to as the "first fixing temperature for color printing").

[0072] If none of the total pixel values ​​of all colors in the N × M blocks exceed the first threshold, the fixing control unit 123 calculates the total sub-scanning pixel value for each CMYK color by summing the total pixel values ​​of each color in the sub-scanning direction of the N blocks arranged in the sub-scanning direction at the k-th block position (where k is an integer between 1 and M) in the main scanning direction, and then calculates the total sub-scanning pixel value for all colors by summing the calculated total sub-scanning pixel values ​​for each CMYK at the k-th block position. For example, if the total pixel values ​​of each CMYK in block 1 arranged in the sub-scanning direction at the k-th block position in the main scanning direction are Ct1, Mt1, Yt1, Kt1, the total pixel values ​​of each CMYK in block 2 are Ct2, Mt2, Yt2, Kt2, the total pixel values ​​of each CMYK in block 3 are Ct3, Mt3, Yt3, Kt3, ..., the fixing control unit 123 calculates the total sub-scanning pixel value for color C as Ct1 + Ct2 + Ct3 + ... First, calculate Mt1+Mt2+Mt3+... as the total pixel value in the sub-scanning direction for the M color, calculate Yt1+Yt2+Yt3+... as the total pixel value in the sub-scanning direction for the Y color, calculate Kt1+Kt2+Kt3+... as the total pixel value in the sub-scanning direction for the K color, and further calculate Ct1+Ct2+Ct3+...+Mt1+Mt2+Mt3+...+Yt1+Yt2+Yt3+...+Kt1+Kt2+Kt3+... as the total pixel value in the sub-scanning direction for all colors.

[0073] The fixing control unit 123 calculates the m-th mean value by averaging the total pixel value of all colors in the sub-scanning direction at the m-th block position (where m is an integer between 1 and M-1) in the main scanning direction with the total pixel value of all colors in the sub-scanning direction at the m+1-th block position in the main scanning direction. If at least one of the m-th mean values ​​exceeds a predetermined threshold (hereinafter referred to as the "third threshold"), the fixing control unit 123 determines the fixing temperature of the fixing unit 13 to a predetermined first fixing temperature for color printing. If none of the m-th mean values ​​exceed the third threshold, the fixing temperature of the fixing unit 13 is determined to a fixing temperature lower than the first fixing temperature for color printing, which is predetermined according to the m-th mean value. In this embodiment, the fixing control unit 123 determines the fixing temperature to a first fixing temperature for color printing if at least one of the first average value to the M-1 average value exceeds the third threshold, and determines the fixing temperature to a predetermined second fixing temperature for color printing that is lower than the first fixing temperature for color printing if none of the first average value to the M-1 average value exceed the third threshold. Based on the determined fixing temperature, the fixing control unit 123 controls the fixing temperature of the fixing unit 13.

[0074] The above describes the processing performed by the fixing control unit 123 in the case of color printing.

[0075] The fuser control unit 123 performs the following processing in the case of monochrome printing.

[0076] The fixing control unit 123 obtains the total pixel values ​​of the K colors for each of the N × M blocks from the image memory 20.

[0077] The fixing control unit 123 calculates the total pixel value of K color in the sub-scanning direction by summing the total pixel values ​​of K color for each of the N blocks arranged in the sub-scanning direction at the k-th block position (where k is an integer between 1 and M) in the main scanning direction.

[0078] The fixing control unit 123 calculates the m-th mean value by averaging the total pixel value of the K color in the sub-scanning direction at the m-th block position (where m is an integer between 1 and M-1) in the main scanning direction with the total pixel value of the K color in the sub-scanning direction at the m+1-th block position in the main scanning direction. If at least one of the m-th mean values ​​exceeds a predetermined threshold (hereinafter referred to as the "second threshold"), the fixing control unit 123 determines the fixing temperature of the fixing unit 13 to a predetermined first fixing temperature for monochrome printing. If none of the m-th mean values ​​exceed the third threshold, the fixing temperature of the fixing unit 13 is determined to a fixing temperature lower than the predetermined first fixing temperature for monochrome printing, according to the m-th mean value. In this embodiment, the fixing control unit 123 determines the fixing temperature to a predetermined first fixing temperature for monochrome printing if at least one of the first average value to the M-1 average value exceeds the second threshold, and determines the fixing temperature to a predetermined second fixing temperature for monochrome printing that is lower than the first fixing temperature for monochrome printing if none of the first average value to the M-1 average value exceed the second threshold. Based on the determined fixing temperature, the fixing control unit 123 controls the fixing temperature of the fixing unit 13.

[0079] The image forming apparatus 1 has use cases such as consolidated printing of multiple pages and printing rotated by 90 degrees. The fixing control unit 123 receives settings for consolidated printing and printing rotated by 90 degrees via the operation unit 16, and can change each of the above processes according to the settings for consolidated printing and printing rotated by 90 degrees. As described above, the image data is divided into N × M blocks of a predetermined size, and N blocks are arranged in a predetermined first direction and M blocks are arranged in a second direction perpendicular to the first direction. For example, in the case of printing rotated by 90 degrees, the first and second directions are the orthogonal direction and the transport direction of the paper P of the transport unit 17, and in this case, the second and first directions become the sub-scanning direction and the main scanning direction, and the same processes as above should be performed. In the case of 90-degree printing, "M" corresponds to "N" as described in the claims, and "N" corresponds to "M" as described in the claims.

[0080] The transport control unit 124 controls the operation of the transport unit 17 to transport the paper P.

[0081] The image formation control unit 125 controls the image formation operation of the image forming unit 12. Specifically, the image formation control unit 12 instructs the image forming unit 12 to develop the electrostatic latent image formed on the surface of the photoreceptor drum by the light emission control unit 122 to generate a toner image, and to transfer the generated toner image to the paper P that is being transported to the image formation position.

[0082] [Determination process for fixing temperature] Figures 7 and 8 are flowcharts showing the processing procedure for determining the fixing temperature of the fixing unit 13 by the fixing control unit 123 in Figure 3. The fixing temperature determination process of the fixing unit 13 by the fixing control unit 123 shown in Figures 7 and 8 is executed according to the fixing temperature control program stored in the storage unit 18.

[0083] The fixing control unit 123 determines whether or not it is monochrome printing according to the settings received via the operation unit 16 (step S101).

[0084] If the fuser control unit 123 determines in the determination process of step S101 that it is monochrome printing (S101: YES), the fuser control unit 123 proceeds to the process of step S102.

[0085] In monochrome printing, the pixel value counting unit 193 counts the K-color pixel values ​​of each of the multiple pixels contained in each of the N×M blocks, based on the K-plane image data input from the color conversion unit 192. In other words, the pixel value counting unit 193 obtains the total K-color pixel value by summing the K-color pixel values ​​of each of the multiple pixels contained in each of the N×M blocks. The total K-color pixel values ​​for each of the N×M blocks are stored in the image memory 20 by processing by the count value transfer unit 194 and the print controller 110.

[0086] The fixing control unit 123 obtains the total pixel values ​​of the K colors for each of the N × M blocks from the image memory 20 (step S102).

[0087] Following the processing in step S102, the fixing control unit 123 calculates the total pixel value of K color in the sub-scanning direction by summing the total pixel values ​​of K color for each of the N blocks arranged in the sub-scanning direction at the k-th block position (where k is an integer between 1 and M) in the main scanning direction (step S103).

[0088] Following the processing in step S103, the fixing control unit 123 calculates the m-th average value by averaging the total pixel value of the K color in the sub-scan direction at the m-th block position (where m is an integer between 1 and M-1) in the main scanning direction and the total pixel value of the K color in the sub-scan direction at the (m+1)-th block position in the main scanning direction (step S104). In this embodiment, the fixing control unit 123 calculates the m-th average value by averaging the total pixel value of the K color in the sub-scan direction at consecutive m-th block positions (where m is an integer between 1 and M-1) in the main scanning direction and the total pixel value of the K color in the sub-scan direction at the (m+1)-th block position while moving the block position in the main scanning direction one block at a time.

[0089] Following the processing in step S104, the fixing control unit 123 determines whether at least one of the first average values ​​to the M-1 average values ​​exceeds the second threshold (step S105). If the fixing control unit 123 determines in the determination process of step S105 that at least one of the first average values ​​to the M-1 average values ​​exceeds the second threshold (S105: YES), the fixing control unit 123 sets the fixing temperature of the fixing unit 13 to the first fixing temperature for monochrome printing (step S106). On the other hand, if the fixing control unit 123 determines in the determination process of step S105 that none of the first average values ​​to the M-1 average values ​​exceed the second threshold (S105: NO), the fixing control unit 123 sets the fixing temperature of the fixing unit 13 to the second fixing temperature for monochrome printing, which is lower than the first fixing temperature for monochrome printing (step S107).

[0090] If the fuser control unit 123 determines in the determination process of step S101 that it is not monochrome printing, that is, color printing (S101: NO), the fuser control unit 123 proceeds to the process of step S108.

[0091] In the case of color printing, the pixel value counting unit 193 counts the pixel values ​​of each of the multiple pixels contained in each of the N×M blocks, based on the image data of each CMYK plane input from the color conversion unit 192. In other words, the pixel value counting unit 193 obtains the total pixel value of each color by summing the pixel values ​​of each of the multiple pixels contained in each of the N×M blocks. Furthermore, the pixel value counting unit 193 counts the CMYK pixel values ​​of each of the multiple pixels contained in each of the N×M blocks, based on the image data of each CMYK plane input from the color conversion unit 192. In other words, the pixel value counting unit 193 obtains the total pixel value of all colors (total pixel value of all colors) by summing the CMYK pixel values ​​of each of the multiple pixels contained in each of the N×M blocks. The total pixel values ​​for each CMYK color and the total pixel values ​​for all colors in each of the N×M blocks are stored in the image memory 20 through processing by the count value transfer unit 194 and the print controller 110.

[0092] The fixing control unit 123 obtains the total pixel values ​​for each CMYK color and the total pixel value for all colors from the image memory 20 (step S108).

[0093] Following the processing in step S108, the fixing control unit 123 determines whether at least one of the total pixel values ​​of all colors in the N×M blocks exceeds a first threshold (step S109). If the fixing control unit 123 determines in the determination process of step S109 that at least one of the total pixel values ​​of all colors in the N×M blocks exceeds a first threshold (S109: YES), the fixing control unit 123 sets the fixing temperature of the fixing unit 13 to a first fixing temperature for color printing (step S113).

[0094] If, in the determination process of step S109, the fixing control unit 123 determines that none of the total pixel values ​​of all colors in the N × M blocks exceed the first threshold (S109: NO), the fixing control unit 123 proceeds to the process of step S110.

[0095] If none of the total pixel values ​​of all colors in the N × M blocks exceed the first threshold, the fixing control unit 123 calculates the total sub-scanning pixel value for each CMYK color by summing the total pixel values ​​of each of the N blocks arranged in the sub-scanning direction at the k-th block position (where k is an integer between 1 and M) in the main scanning direction, and then calculates the total sub-scanning pixel value for all colors by summing the calculated total sub-scanning pixel values ​​for each CMYK at the k-th block position (step S110).

[0096] Following the processing in step S110, the fixing control unit 123 calculates the m-th average value by averaging the total pixel value of all colors in the sub-scanning direction at the m-th block position (where m is an integer between 1 and M-1) in the main scanning direction and the total pixel value of all colors in the sub-scanning direction at the (m+1)-th block position in the main scanning direction (step S111). In this embodiment, the fixing control unit 123 calculates the m-th average value by averaging the total pixel value of all colors in the sub-scanning direction at consecutive m-th block positions (where m is an integer between 1 and M-1) in the main scanning direction and the total pixel value of all colors in the sub-scanning direction at the (m+1)-th block position while moving the block position in the main scanning direction one block at a time.

[0097] Following the processing in step S111, the fixing control unit 123 determines whether at least one of the first average values ​​to the M-1 average values ​​exceeds the third threshold (step S112). If the fixing control unit 123 determines in the determination process of step S112 that at least one of the first average values ​​to the M-1 average values ​​exceeds the third threshold (S112: YES), the fixing control unit 123 sets the fixing temperature of the fixing unit 13 to the first fixing temperature for color printing (step S113). On the other hand, if the fixing control unit 123 determines in the determination process of step S112 that none of the first average values ​​to the M-1 average values ​​exceed the second threshold (S112: NO), the fixing control unit 123 sets the fixing temperature of the fixing unit 13 to the second fixing temperature for color printing, which is lower than the first fixing temperature for color printing (step S114).

[0098] [Operation] The following describes the image formation flow, including the processes from step S1 to step S8, primarily with reference to Figure 9.

[0099] (1) Image processing and paper transport operation The system controller 190, print controller 110, and engine controller 120 perform control to execute image processing and paper transport operations in parallel, as described below.

[0100] In step S1, when the image generation unit 191 receives a print command written in PDL from, for example, the host PC 23 via the communication unit 22, it performs RIP processing to generate color-represented raster data based on the print command. The image generation unit 191 divides the generated raster data into N × M blocks of a predetermined size, which serve as image processing units, and stores them in the page memory area of ​​the image memory 20.

[0101] In step S2, the color conversion unit 192 generates image data for four planes corresponding to each CMYK color based on the raster data stored in the page memory area of ​​the image memory 20 in the case of color printing, and outputs it to the pixel value count unit 193. In the case of monochrome printing, the color conversion unit 192 generates image data for one plane corresponding to the K color based on the raster data, and outputs it to the pixel value count unit 193.

[0102] In step S3, in the case of color printing, the pixel value counting unit 193 stores the image data for each CMYK plane input from the color conversion unit 192 in the page memory area of ​​the image memory 20. At this time, when the pixel value counting unit 193 has stored the image data for all four planes in the page memory area of ​​the image memory 20, it outputs a print ready signal to the print controller 110.

[0103] In monochrome printing, the pixel value counting unit 193 stores the K-plane image data input from the color conversion unit 192 in the page memory area of ​​the image memory 20. At this time, when the pixel value counting unit 193 has stored the image data for one plane in the page memory area of ​​the image memory 20, it outputs a print ready signal to the print controller 110.

[0104] When the print controller 110 receives a print readiness signal for both color and monochrome printing, it notifies the engine controller 120 that the print readiness is complete. When the engine controller 120 receives the print readiness notification, its transport control unit 124 instructs the transport unit 17 to start transporting the paper P.

[0105] In step S4, the rotation and aggregation unit 195, in the case of color printing, refers to the image data of each CMYK plane stored in the page memory area of ​​the image memory 20, and in the case of monochrome printing, refers to the image data of the K plane stored in the page memory area of ​​the image memory 20, reads block-unit image data from the image memory 20 while controlling the reading order, and performs at least one of rotation and aggregation processing by rearranging the read block-unit image data according to the settings received via the operation unit 16.

[0106] In step S5, the correction processing unit 196 performs correction processing, such as edge processing and gamma correction, on the block-level image data in the order in which the processing by the rotation and aggregation unit 195 is completed.

[0107] In step S6, the screen processing unit 197 performs screen processing on the block-based image data in the order in which the processing by the correction processing unit 196 is completed. The screen processing unit 197 converts the block-based image data for one page that has been screen processed into final drawing data and stores it in the image memory 20 which functions as a buffer.

[0108] At this time, the screen processing unit 197 outputs a "drawing data ready" signal to the print controller 110 when it has saved the drawing data to the image memory 20. When the print controller 110 receives the "drawing data ready" signal, it notifies the engine controller 120 that the drawing data is ready. When the engine controller 120 receives the notification that the drawing data is ready, the transport control unit 124 of the engine controller 120 instructs the transport unit 17 to continue transporting the paper P.

[0109] (2) Imaging operation The engine controller 120 performs control to execute the image formation operation as follows.

[0110] In step S7, the print position adjustment unit 121 reads drawing data from the image memory 20 and, according to the settings received via the operation unit 16, performs at least one of the following on the read drawing data: image position adjustment processing and margin addition processing.

[0111] In step S8, the light emission control unit 122 controls the light emission of the LSU 12A by switching the on / off status of the lighting signal based on the drawing data from which at least one of the image position adjustment process and the margin addition process has been performed.

[0112] The image formation control unit 125 controls the image formation operation of the image forming unit 12. Specifically, the image formation control unit 12 instructs the image forming unit 12 to develop the electrostatic latent image formed on the surface of the photoreceptor drum by the light emission control unit 122 to generate a toner image, and to transfer the generated toner image to the paper P that is being transported to the image formation position.

[0113] (3) Fixing operation The system controller 190, print controller 110, and engine controller 120 perform control for fixing temperature control and fixing operation as follows.

[0114] In step S3, in the case of color printing, the pixel value counting unit 193, based on the image data of each CMYK plane input from the color conversion unit 192, obtains the total pixel value of each CMYK color in each of the N×M blocks by summing the pixel values ​​of each of the multiple pixels in that block. Furthermore, it obtains the total pixel value of all colors in each of the N×M blocks by summing the pixel values ​​of each of the CNYK colors in each of the multiple pixels in that block. The pixel value counting unit 193 then outputs the total pixel value of C color, the total pixel value of M color, the total pixel value of Y color, the total pixel value of K color, and the total pixel value of all colors for each of the N×M blocks to the count value transfer unit 194 in a predetermined order.

[0115] The count value transfer unit 194 stores the total pixel values ​​for C color, M color, Y color, K color, and the total pixel values ​​for all colors for each block, which are input from the pixel value count unit 193 in a predetermined order, into the SRAM of the system controller 190 in the order they were input. The count value transfer unit 194 then outputs an interrupt signal to the print controller 110 when it has stored the total pixel values ​​for C color, M color, Y color, K color, and the total pixel values ​​for all colors for a predetermined number of blocks in the SRAM. When an interrupt signal is input, the print controller 110 reads out the total pixel values ​​for C color, M color, Y color, K color, and the total pixel values ​​for all colors from a predetermined number of blocks stored in the SRAM, and stores the read total pixel values ​​for C color, M color, Y color, K color, and the total pixel values ​​for all colors from the predetermined number of blocks in the order they were stored in the SRAM at consecutive addresses in the image memory 20.

[0116] In monochrome printing, the pixel value counting unit 193 obtains the total K-color pixel value for each of the N×M blocks, based on the K-plane image data input from the color conversion unit 192, by summing the K-color pixel values ​​of the multiple pixels contained in that block. The pixel value counting unit 193 then outputs the total K-color pixel value for each of the N×M blocks to the count value transfer unit 194 in a predetermined order.

[0117] The count value transfer unit 194 stores the total K-color pixel values ​​of each block, which are input from the pixel value count unit 193 in a predetermined order, into the SRAM of the system controller 190 in the order they were input. The count value transfer unit 194 then outputs an interrupt signal to the print controller 110 when it has stored the total K-color pixel values ​​of a predetermined number of blocks in the SRAM. When the interrupt signal is received, the print controller 110 reads out the total K-color pixel values ​​of a predetermined number of blocks stored in the SRAM all at once and stores the read total K-color pixel values ​​of the predetermined number of blocks in the order they were stored in the SRAM at consecutive addresses in the image memory 20.

[0118] The fixing control unit 123 determines the fixing temperature of the fixing unit 13 by executing the fixing temperature determination process for the fixing unit 13 shown in Figures 7 and 8, based on the total pixel values ​​of each color and the total pixel values ​​of all colors of each block stored in the image memory 20, or the total pixel values ​​of the K color of each block stored in the image memory 20. Then, based on the determined fixing temperature of the fixing unit 13, the fixing control unit 123 controls the fixing temperature of the fixing unit 13 and heats and pressurizes the paper P on which the toner image has been formed to fix the toner image to the paper P.

[0119] According to the above embodiment, the fixing temperature of the fuser unit 13 is determined using the m-th mean value, which is the average of the sum of the pixel values ​​obtained by summing the pixel values ​​of each of the multiple pixels contained in each of the N blocks arranged in the sub-scanning direction at the m-th block position in the main scanning direction (where m is an integer between 1 and M-1) or the sum of the pixel values ​​for each CMYK color of the multiple pixels contained in that block, and the sum of the sum of the pixel values ​​obtained by summing the pixel values ​​of each of the multiple pixels contained in each of the N blocks arranged in the transport direction at the (m+1)-th block position in the orthogonal direction, or the sum of the pixel values ​​obtained by summing the pixel values ​​for each CMYK color of the multiple pixels contained in that block. The maximum variation in the m-th mean value is suppressed regardless of the positional relationship of the image drawing area on the page to the blocks into which the image data is divided. Therefore, by controlling the fixing temperature of the fuser unit 13, power consumption in the fuser unit 13 can be reduced and the toner image can be reliably fixed to the paper.

[0120] Furthermore, for example, the amount of heat required for fixing differs depending on whether the solid patches of each CMYK color shown in Figure 6(A) are aligned in different sub-scanning directions at the same main scanning direction, or whether the solid patches of each CMYK color shown in Figure 6(B) are located in the same sub-scanning direction at the same main scanning direction. In the case of color printing, determining the fixing temperature of the fixing unit 13 requires using the total pixel value of all colors, which is the sum of the CMYK pixel values ​​of each of the multiple pixels contained in each of the N×M blocks. This enables appropriate fixing temperature control of the fixing unit 13.

[0121] Furthermore, by storing the total pixel values ​​of each of the N×M blocks (the total pixel values ​​of each CMYK color and the total pixel value of all colors in the case of color printing, and the total pixel value of the K color in the case of monochrome printing) in the image memory 20 at consecutive addresses, the determination unit that determines the position corresponding to each of the N×M blocks does not require any additional hardware, thus suppressing an increase in hardware resources.

[0122] Furthermore, the present invention is not limited to the configuration of the above embodiment, and various modifications are possible.

[0123] For example, in the above embodiment, if at least one of the total pixel values ​​of all colors of the N×M blocks (the sum of the CMYK pixel values ​​of multiple pixels included in the block) exceeds a first threshold (S109:YES), the fixing temperature of the fixing unit 13 is determined to be a first fixing temperature for color printing (step S113). If none of the total pixel values ​​of all colors of the N×M blocks exceed the first threshold (S109:NO), the process proceeds to step S110. However, the embodiment is not limited to this. For example, it may be as follows: Following step S108, the fixing control unit 123 calculates the nm average value by averaging the total image value of all colors of the block at the nth block position in the sub-scanning direction (where n is an integer from 1 to N) and the mth block position in the main scanning direction (where m is an integer from 1 to M-1) and the total image value of all colors of the block at the nth block position in the sub-scanning direction and the m+1th block position in the main scanning direction. The fixing control unit 123 may, instead of step S109, determine whether at least one of the average values ​​of the nm (where n is an integer between 1 and N and m is an integer between 1 and M-1) exceeds a predetermined threshold (hereinafter referred to as the "fourth threshold" as appropriate). If it determines that at least one exceeds the fourth threshold, it sets the fixing temperature of the fixing unit 13 to the first fixing temperature for color printing (step S113). If it determines that none exceed the fourth threshold, it proceeds to step S110.

[0124] Furthermore, in the above embodiment, if at least one of the total pixel values ​​of all colors in the N×M blocks exceeds a first threshold, the fixing temperature of the fixing unit 13 is set to a first fixing temperature for color printing; if none of the total pixel values ​​of all colors in the N×M blocks exceed the first threshold, and at least one of the m-th average values ​​exceeds a third threshold, the fixing temperature is set to a first fixing temperature for color printing; and if none of the m-th average values ​​exceed the third threshold, the fixing temperature is set to a second fixing temperature for color printing that is lower than the first fixing temperature for color printing. However, the embodiment is not limited to this. For example, if at least one of the total pixel values ​​of all colors in N×M blocks exceeds a first threshold, the fixing temperature of the fixing unit 13 may be set to a first fixing temperature for color printing. If none of the total pixel values ​​of all colors in N×M blocks exceed the first threshold, and at least one of the m-th mean values ​​exceeds a third threshold, the fixing temperature may be set to a third fixing temperature for color printing that is lower than the first fixing temperature for color printing. If none of the m-th mean values ​​exceed the third threshold, the fixing temperature may be set to a fourth fixing temperature for color printing that is lower than the third fixing temperature for color printing. Alternatively, for each of the multiple intervals separated by a predetermined set of thresholds (two or more), a fixing temperature is predetermined for each interval with a larger value, and the fixing temperature determined for each of the multiple intervals is less than or equal to the first fixing temperature for color printing. The fixing control unit 123 may set the fixing temperature of the fixing unit 13 to the fixing temperature corresponding to the interval containing the largest m-th mean value if none of the total pixel values ​​of all colors in N×M blocks exceed the first threshold.

[0125] Furthermore, in the above modified example, if at least one of the average nm values ​​exceeds the fourth threshold, the fixing temperature of the fixing unit 13 is determined to be the first fixing temperature for color printing; if none of the average nm values ​​exceed the first threshold, and at least one of the m-value values ​​exceeds the third threshold, the fixing temperature is determined to be the first fixing temperature for color printing; and if none of the m-value values ​​exceed the third threshold, the fixing temperature is determined to be the second fixing temperature for color printing, which is lower than the first fixing temperature for color printing. However, the method is not limited to this. For example, if at least one of the average nm values ​​exceeds the fourth threshold, the fixing temperature of the fixing unit 13 is determined to be the first fixing temperature for color printing; if none of the average nm values ​​exceed the first threshold, and at least one of the m-value values ​​exceeds the third threshold, the fixing temperature is determined to be the third fixing temperature for color printing, which is lower than the first fixing temperature for color printing; and if none of the m-value values ​​exceed the third threshold, the fixing temperature is determined to be the fourth fixing temperature for color printing, which is lower than the third fixing temperature for color printing. Furthermore, for each of the multiple intervals separated by a predetermined set of thresholds (two or more), a fixing temperature is predetermined for each interval with a larger value, and the fixing temperature predetermined for each of the multiple intervals is less than or equal to the first fixing temperature for color printing. The fixing control unit 123 may also determine the fixing temperature of the fixing unit 13 to the fixing temperature corresponding to the interval containing the largest m-value if none of the nm-value averages exceed the first threshold.

[0126] Furthermore, in the above embodiment, the determination process in step S109 uses one of the first thresholds as a threshold to determine the fixing temperature of the fixing unit 13. However, the method is not limited to this, and multiple thresholds may be prepared to control the fixing temperature of the fixing unit 13 in multiple stages, such that the fixing temperature of the fixing unit 13 increases as it exceeds a threshold with a large maximum total pixel value, and proceeds to step S110 if it does not exceed the smallest threshold. Also, in the above modified example, the determination process that replaces the determination process in step S109 uses one of the fourth thresholds as a threshold to determine the fixing temperature of the fixing unit 13. However, the method is not limited to this, and multiple thresholds may be prepared to control the fixing temperature of the fixing unit 13 in multiple stages, such that the fixing temperature of the fixing unit 13 increases as it exceeds a threshold with a large maximum average value of the nanometer, and proceeds to step S110 if it does not exceed the smallest threshold.

[0127] Furthermore, in the above embodiment, the fixing temperature determination process for the fixing unit 13 in Figures 7 and 8 is performed by the fixing control unit 123 of the engine controller 120. However, the embodiment is not limited to this, and the print controller 110 may perform the fixing temperature determination process for the fixing unit 13 in Figures 7 and 8, notify the fixing control unit 123 of the engine controller 120 of the determined fixing temperature, and the fixing control unit 123 may perform temperature control of the fixing unit 13 based on the notified fixing temperature.

[0128] Furthermore, the fixing temperature of the fixing unit 13 is determined by various parameters other than whether it is color printing or monochrome printing, such as the weight of the paper, the printing speed (slowdown during silent mode or high-resolution printing), the operating environment of the image forming apparatus 1 (high temperature environment, low temperature environment), and the image quality mode (glossy mode, etc.). Therefore, the fixing temperature may be determined by a combination of these parameters.

[0129] Furthermore, the configurations and processes shown in the above embodiments using Figures 1 to 9, and the configurations and processes shown in the modified examples, are merely embodiments of one invention, and the present invention is not intended to be limited to these configurations and processes. [Explanation of Symbols]

[0130] 1. Image forming apparatus 12 Image forming unit 13 Fixing section 17 Conveying Section 123 Fixing Control Unit 193 Pixel value counting section

Claims

1. An image forming unit that forms a toner image on paper based on image data, A fixing unit that heats and pressurizes the paper on which the toner image is formed, A transport unit that transports the aforementioned paper to the image forming unit and the fixing unit, A control unit for controlling the fixing temperature of the fixing section, Equipped with, The control unit, In each of the N × M blocks obtained by dividing the aforementioned image data into predetermined sizes, a total pixel value acquisition process is performed to obtain the total pixel value by summing the pixel values ​​of each of the multiple pixels contained in that block. The N × M blocks are arranged in the paper transport direction of the transport unit in an N-order configuration and in an orthogonal direction perpendicular to the transport direction. At the m-th block position in the orthogonal direction (where m is an integer from 1 to M-1), an average value calculation process is performed to calculate the m-th average value by averaging the sum of the total pixel values ​​of the N blocks arranged in the transport direction and the sum of the total pixel values ​​of the N blocks arranged in the transport direction at the (m+1)th block position in the orthogonal direction. If at least one of the aforementioned average values ​​of m exceeds a predetermined threshold, the fixing temperature of the fixing unit is determined to a predetermined first fixing temperature. If none of the aforementioned average values ​​of m exceed the predetermined threshold, the fixing temperature of the fixing unit is determined to a fixing temperature lower than the first fixing temperature, which is predetermined according to the aforementioned average values ​​of m. Image forming apparatus.

2. An image forming unit that forms a toner image on paper using multiple colors based on image data, A fixing unit that heats and pressurizes the paper on which the toner image is formed, A transport unit that transports the aforementioned paper to the image forming unit and the fixing unit, A control unit for controlling the fixing temperature of the fixing section, Equipped with, The control unit, In each of the N × M blocks obtained by dividing the aforementioned image data into predetermined sizes, a total pixel value acquisition process is performed to obtain the total pixel value of each color by summing the pixel values ​​of each of the multiple pixels of that color contained in that block. The N × M blocks are arranged in the paper transport direction of the transport unit in an N-order configuration and in an orthogonal direction perpendicular to the transport direction, and an average value calculation process is performed to calculate the m-average value by averaging the sum of the total pixel values ​​of each of the multiple colors in each of the N blocks arranged in the transport direction and the sum of the total pixel values ​​of each of the multiple colors in each of the N blocks arranged in the transport direction at the (m+1)-th block position in the orthogonal direction. If at least one of the aforementioned average values ​​of m exceeds a predetermined threshold, the fixing temperature of the fixing unit is determined to a predetermined first fixing temperature. If none of the aforementioned average values ​​of m exceed the predetermined threshold, the fixing temperature of the fixing unit is determined to a fixing temperature lower than the first fixing temperature, which is predetermined according to the aforementioned average values ​​of m. Image forming apparatus.

3. The control unit, In the process of obtaining the total pixel value, in each of the N × M blocks, for each of the colors, the total pixel value of that color is obtained by summing the pixel values ​​of each of the multiple pixels of that color contained in the block, and further, the total pixel value of all colors is obtained by summing the pixel values ​​of each of the multiple pixels of that color contained in the block. A determination process is performed to determine whether at least one of the total pixel values ​​of all colors in the N × M blocks exceeds a predetermined first threshold. In the determination process described above, if it is determined that at least one of the total pixel values ​​of all colors in the N × M blocks exceeds the first threshold, the fixing temperature of the fixing unit is set to a predetermined fixing temperature that is equal to or greater than the first fixing temperature. If, in the determination process, it is determined that none of the total pixel values ​​of all colors in the N × M blocks exceed the first threshold, the average value calculation process and the fixing temperature determination process are performed. The image forming apparatus according to claim 2.

4. The control unit, In the process of obtaining the total pixel value, in each of the N × M blocks, for each of the colors, the total pixel value of that color is obtained by summing the pixel values ​​of each of the multiple pixels of that color contained in the block, and further, the total pixel value of all colors is obtained by summing the pixel values ​​of each of the multiple pixels of that color contained in the block. A second mean calculation process is performed to calculate the n-m mean value by averaging the total color image value of the block at the nth block position (where n is an integer from 1 to N) in the transport direction and the mth block position (where m is an integer from 1 to M-1) in the orthogonal direction, and the total color image value of the block at the nth block position in the transport direction and the m+1th block position in the orthogonal direction. A determination process is performed to determine whether at least one of the n-m average values ​​exceeds a predetermined first threshold. In the determination process described above, if it is determined that at least one of the n-m average values ​​exceeds the first threshold, the fixing temperature of the fixing unit is set to a predetermined fixing temperature that is equal to or greater than the first fixing temperature. In the determination process, if it is determined that none of the n-m average values ​​exceed the first threshold, the average value calculation process and the fixing temperature determination process are performed. The image forming apparatus according to claim 2.

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